Fiber deposition in the tracheobronchial region: deposition equations.

A lung deposition model for fibrous aerosol needs accurate deposition equations for different regions of the human respiratory tract. For fiber deposition in the tracheobronchial region there are several theoretical and empirical equations to predict deposition efficiency in the impaction-dominant region. However, few were verified with experimental data. We have obtained experimental data of fiber deposition in realistic human airway replicas using carbon fibers. Comparison of experimental data and existing deposition models yield variable results, with some models performing better than other models. There was no consistent agreement found over the Stokes number range of experimental data. A generic empirical model for fiber deposition in the tracheobronchial region was developed based on all carbon fiber deposition data in human lung replicas. This model includes the size of fibers and the geometry of the tracheobronchial bifurcation. Because it is difficult to develop only one equation for all data from the trachea to the major bronchial bifurcations, the deposition patterns in the trachea and first generation were each predicted by their own equations. An additional equation was developed for the second to fourth generations. This model, combined with oral and nasal deposition predictions which will be published elsewhere, can be used to investigate the inhalation dosimetry and deposition patterns of fibers in human lungs for assessing occupational hazards and air pollutants.